Lockheed XF-104

Lockheed XF-104

infobox Aircraft
name = XF-104
type = Interceptor prototype
manufacturer = Lockheed Aircraft Corporation




caption = Lockheed XF-104 FG-786
designer= Clarence L "Kelly" Johnson
first flight=4 March avyear|1954
primary user= Lockheed
more users= United States Air Force
introduction=
retired=
number built= Two
status=
unit cost=
variants with their own articles= F-104 Starfighter
Lockheed NF-104A
Canadair CF-104
Aeritalia F-104S
CL-1200 Lancer/X-27

The Lockheed XF-104 was a single-engine, high-performance, supersonic interceptor aircraft designed as the prototype for a United States Air Force series of lightweight and simple fighters.Only two aircraft were built, one aircraft was used primarily for aerodynamic research and the other served as an armament testbed.Bowman 2000, p. 33.] Both prototypes were destroyed in accidents during testing. The XF-104 was the forerunner of over 2,500 F-104 Starfighters.

Development

Clarence L "Kelly" Johnson, chief engineer at Lockheed's Skunk Works, visited Korea in December 1951 and talked to fighter pilots about what sort of aircraft they wanted. At the time USAF pilots were confronting the MiG-15 "Fagot" in their F-86 Sabres, and many of the pilots felt that the MiGs were superior to the larger and more complex American design. The pilots requested a small and simple aircraft with excellent performance.Bowman 2000, p. 26.]

One pilot in particular, Colonel Gabby Gabreski was quoted as saying; "I'd rather sight with a piece of chewing gum stuck on the windscreen" and told Johnson that Radar "was a waste of time".Bowman 2000, p. 26.]

On his return to the U.S., Johnson immediately started the design of just such an aircraft realising that an official requirement would soon be published. In March 1952 his team was assembled, and they sketched several different aircraft proposals, ranging from small designs at 8,000 lb (3.6 t), to fairly large ones at 50,000 lb (23 t). The L-246 as the design became known remained essentially identical to the "Model L-083 Starfighter" as eventually delivered.Bowman 2000, p. 32.]

Design approval and competition

The design was presented to the Air Force in November 1952, who were interested enough to create a new proposal, inviting several companies to participate. Three additional designs were received: the Republic AP-55, an improved version of its prototype XF-91 Thunderceptor; the North American NA-212, which would eventually evolve into the F-107; and the Northrop N-102 "Fang", a new General Electric J79-powered design. Although all were interesting, Lockheed had an insurmountable lead and was granted a development contract in March 1953.Bowman 2000, p. 32.]

Test data from the earlier Lockheed X-7 unmanned ramjet/rocket program proved invaluable for aerodynamic research since the XF-104 would share the X-7's wing and tail planform and airfoil sections. [Reed 1981, p. 10.] Upton 2003, p. 13.] Experience gained from the Douglas X-3 Stiletto was also used in the design phase of the XF-104.Bowman 2000, p. 27.] Over 400 surplus instrumented artillery rockets were launched to test various airfoils and tail designs; from which the camera film and telemetry were recovered by parachute.Upton 2003, p. 14.]

Work progressed quickly, with a wooden mock-up ready for inspection at the end of April, and work started on two prototypes late in May. At the time, the J79 engine was not ready; so, both prototypes were designed to use the Wright J65 engine instead, a licensed built version of the Armstrong Siddeley Sapphire. Construction of the first prototype XF-104 (53-7786) began in summer 1953 at Lockheed's Burbank, California factory. This aircraft was powered by a non-afterburning Buick-built Wright J65-B-3 turbojet. The first prototype was completed by early 1954, and started flying in March. The total time from award of the contract to first flight was only one year, a very short time even then, and unheard of today, when ten to 15 years is more typical.Upton 2003, p. 13.]

Construction of the second prototype (53-7787) began in autumn 1953.

Design

In order to achieve the desired performance, Lockheed chose a minimalist approach: a design that would achieve high performance by wrapping the lightest, most aerodynamically efficient airframe possible around a single powerful engine. The emphasis was on minimizing drag and mass.Bowman 2000, p. 29.]

Wing

The XF-104 had a radical wing design. Most jet fighters of the period (and to this day) used a swept-wing or delta-wing planform. This allowed a reasonable balance between aerodynamic performance, lift, and internal space for fuel and equipment. Lockheed's tests, however, determined that the most efficient shape for high-speed, supersonic flight was a very small, straight, mid-mounted, trapezoidal wing. The wing was extremely thin, with a thickness-to-chord ratio of only 3.36%. Its aspect ratio was 2.45. The leading edges of the wing were so thin (0.016 in / 0.41 mm) and so sharp that they presented a hazard to ground crews, and protective guards had to be installed during ground operations. The thinness of the wings meant that fuel tanks and landing gear had to be contained in the fuselage. The hydraulic actuators driving the ailerons were only one inch (25 mm) thick to fit into the available space and were known as Piccolo actuators because of their resemblance to this musical instrument. The wings had electrically driven leading and trailing edge flaps to increase lift at low speed. The XF-104 did not feature the Boundary Layer Control System of the production aircraft.Bowman 2000, p. 28.]

Tail surfaces

After extensive wind tunnel testing, the stabilator was mounted at the top of the fin for optimum stability and control about the pitch axis.Bowman 2000, p. 28.] Because the vertical tail fin was only slightly shorter than the length of each wing and nearly as aerodynamically effective, it could act as a wing on rudder application (a phenomenon known as Dutch roll). To offset this effect, the wings were angled downward to give 10° anhedral. The rudder was manually operated and supplemented by a small yaw damper surface mounted at the bottom of the fin.Bowman 2000, p. 28.]

Fuselage

The fuselage of the XF-104 had a high fineness ratio, i.e., tapering sharply towards the nose, and a small frontal area of 25 sq-ft. [Upton 2003, p. 17.] The fuselage was tightly packed, containing the cockpit, avionics, cannon, all internal fuel, landing gear, and engine.Bowman 2000, p. 29.]

The air intakes, designed by Ben Rich, were of fixed geometry without inlet cones, since the J65-powered aircraft was incapable of Mach 2 performance. They were similar to those of the F-94 Starfire, being mounted slightly away from the fuselage, with an inner splitter plate for the boundary layer bleed air.

The combination of these features provided extremely low drag except at high angle of attack, at which point induced drag became very high.

Ejection seat

The XF-104 featured an unusual downward-ejecting Stanley B seat. It was feared that contemporary ejection seat designs would not have enough explosive power to clear the high "T" tail assembly. In the event of the seat not firing it was possible to manually release the lower fuselage hatch and then exit the aircraft via gravity. The F-104 series aircraft would later convert to upward-ejecting seats but the fuselage hatch was retained as a useful maintenance feature.Bowman 2000, p. 33.] [cite web|url=http://www.ejectionsite.com/frame_sg.htm|title=Ejection seats of the F-104]

Differences between XF-104 and F-104 Starfighter

Visible changes from the XF-104 to production versions of the Starfighter include a longer fuselage (to accommodate the J79 engine and extra internal fuel) and a forward-retracting nose landing gear (except two-seat versions) to increase clearance for the downward-ejecting seat. A ventral fin for increased stability was added during the YF-104A test programme. Inlet shock cones and a fuselage spine fairing between the canopy and fin were further added features.Bowman 2000, p. 32.] Upton 2003, p. 38.]

Testing and evaluation

First XF-104-LO

The first XF-104 (Lockheed 083-1001, USAF "53-7786") was taken by road to Edwards Air Force Base amidst high secrecy during the night of 24-25 FebruaryBowman 2000, p. 32.] where Lockheed test pilot Tony LeVier was to do the initial testing. On February 28 1954, the XF-104 made a planned hop [Pace 1992, p.17.] of about five feet off the ground during a high-speed taxi, but its first official flight took place on 4 March 1954. During that flight, the landing gear would not retract, and LeVier landed after a low-speed flight of about 20 minutes. After adjustments, LeVier took off again but the landing gear still would not retract. The problem turned out to be low pressure in the hydraulic system. Bad weather kept the XF-104 on the ground until 26 March when further flights were carried out with the landing gear retracting normally.

Of the two aircraft FG-786 was used primarily for aerodynamic testing and was the only XF-104 to be used for tip-tank carriage and jettison trials.

The yaw damper of the XF-104 was found to be ineffective and the rudder did not positively center, these problems were corrected by revising the rudder control system.Pace 1992, p. 20.]

The XF-104 was subsonic in level flight when powered by the non-afterburning J65, but Mach 1 could be easily exceeded during a slight descent. In July 1954, the J65-B-3 was replaced by the afterburning J65-W-7 turbojet. With this engine installed the performance of the XF-104 was greatly improved. Maximum level speed was Mach 1.49 at convert|41000|ft|m, and an altitude of convert|55000|ft|m could be attained in a zoom climb, while Mach 1.6 could be attained in a dive. XF-104 "number 1" achieved a top speed of Mach 1.79 at convert|60000|ft|m on 25 March 1955 with Lockheed test pilot J. Ray Goudey at the controls. This was the highest speed achieved by either of the XF-104 prototypes.Bowman 2000, p. 29.] The first XF-104 was accepted by the USAF in November 1955.

XF-104 53-7786 was lost in a crash on 11 July 1957 when it developed an uncontrollable tail flutter while flying chase for F-104A flight tests. The entire tail group was ripped from the airframe, and Lockheed test pilot Bill Park was forced to eject. Vertical fin flutter was a known problem and the aircraft had been limited to speeds of no more than Mach 0.95 at the time of the accident. Tony LeVier had attempted to have the aircraft removed from flight status and placed in a museum, arguing that its performance was not suitable for chase duties.Bowman 2000, p. 35.] Upton 2003, p. 45.] Pace 1992, p. 22.]

econd XF-104-LO

The second prototype (Lockheed 083-1002, USAF "53-7787"), which was fitted with the afterburning J65 from the start, first flew on 5 October 1954. Since it was to be the armament test bed, it was fitted with the 20 mm Vulcan cannon and was equipped with an AN/ASG-14T-1 fire control system.Upton 2003, p. 38.]

Initial aerial firing tests with the Vulcan cannon were successful, but on 17 December, there was an explosion during a firing burstBowman 2000, p. 35.] and the J65 engine suffered severe compressor stalls. Test pilot Tony LeVier immediately shut down the engine and glided back to make a successful deadstick landing at Rogers Dry Lake. An investigation later showed that one of the 20 mm cannon rounds had exploded in the breech, blowing the bolt out the rear of the gun and through the structure into the forward fuselage fuel cell. Jet fuel had run into the gun bay, and leaked out of the compartment door seals and into the left engine air intake. The engine immediately flooded with fuel, causing the compressor stalls.

XF-104 53-7787 was lost on 14 April 1955 after accumulating over 1,000 flying hoursBowman 2000, p. 35.] [Kinzey 1991, p. 6.] when test pilot Herman Salmon was forced to eject during gun firing trials at convert|50000|ft|m. The gun malfunctioned during a test firing, and severe vibrations began to build up which knocked loose the ejection hatch below the cockpit. Cabin pressure was lost with Salmon's pressure suit inflating and covering his face so that he could not see. Recalling Tony LeVier's harrowing experience with the exploding cannon shell the previous December, Salmon believed that the same thing had happened to him and that he had no option but to eject. He later found out that he could have saved 53-7787 by simply bringing it down to a lower altitude and waiting for his pressure suit to deflate. With the loss of the armament testbed, Lockheed engineers were forced to find an alternative, and armament trials were continued on a modified Lockheed F-94C Starfire.Pace 1992, p. 20.] Consequently, no XF-104 prototype survives today.

Testing conclusions

Flight testing proved that performance estimates were accurate and that even when fitted with the low powered J65 engine, the XF-104 flew faster than the other Century Series fighters being developed at the time. The XF-104's ceiling at convert|60000|ft|m was convert|7000|ft|m higher than predicted, and it exceeded estimated speed and drag figures by two to three percent. [Kinzey 1991, p. 4.] It was noted however that the low thrust of the J65 engine did not enable the full performance potential of the type to be realized..Bowman 2000, p. 35.]

The unpowered rudder did not provide adequate directional control at high airspeeds (remedied by using hydraulic power on all subsequent versions of the F-104) and some concern was expressed over poor subsonic maneuverability at higher altitudes.Pace 1992, p. 20.]

Production aircraft would feature a redesigned fin structure using stainless steel spars to eliminate the flutter problem.Upton 2003, p. 45.] Since the internal fuel capacity was low limiting the useful range of the aircraft, extra capacity was provided on later versions by lengthening the forward fuselage.Bowman 2000, p. 35.]

During a later interview Kelly Johnson was asked about his opinion on the aircraft, "Did it come up to my designs? In terms of performance, yes. In terms of engine, we went through a great many engine problems, not with the J65s but with the J79s." [Reed 1981, p. 13.]

For his part in designing the F-104 airframe Johnson was jointly awarded the Collier Trophy in 1958, sharing the honor with General Electric (engine) and the U.S. Air Force (Flight Records). [ [http://www.naa.aero/html/awards/index.cfm?cmsid=155 Collier Trophy winners, 1950-1959] , National Aeronautic Association.]

Variants

Approval of the XF-104 design led to a contract for 17 YF-104A service test aircraftBowman 2000, p. 35.] and a production run of over 2,500 units built both in the United States and under license worldwide.

Operators

;USA
* Lockheed
* United States Air Force

pecifications (XF-104)

aircraft specifications
plane or copter?= plane
jet or prop?= jet

ref=BowmanBowman 2000, p. 33.] and Drendel, [Drendel 1976, p. 10.]
crew=1
length main= 49 ft 2 in
length alt= 15 m
span main= 21 ft 11 in
span alt= 6.69 m
height main= 13 ft 6 in
height alt= 4.1 m
area main= 196 ft²
area alt= 18.21 m²
airfoil= Bi-convex 3.36%
empty weight main= 11,500 lb
empty weight alt= 5,216 kg
loaded weight main= 16,700 lb
loaded weight alt= 7,575 kg
max takeoff weight main= 15,700 lb
max takeoff weight alt= 7,120 kg
more general=
engine (jet)= Wright J65
type of jet= turbojet
number of jets=1
thrust main= 7,800 lbf
thrust alt= 34.70 kN
thrust original=
afterburning thrust main= 10,300 lbf
afterburning thrust alt= 45.82 kN|
max speed main= 1,151 knots
max speed alt= 1,324 mph, 2,131 km/h
cruise speed main=
cruise speed alt=
never exceed speed main=
never exceed speed alt=
stall speed main= 139 knots
stall speed alt= 160 mph, 257 km/h
range main= 695 nmi
range alt= 800 mi, 1,290 km
ceiling main= 50,500 ft
ceiling alt= 15,500 m
climb rate main=
climb rate alt=
loading main=
loading alt=
thrust/weight=
power/mass main=
power/mass alt=
more performance=
armament= * One M61 Vulcan 20 mm cannon (XF-104 083-1002 only)
avionics=

ee also

aircontent
related=
* F-104 Starfighter
* Lockheed NF-104A
* Canadair CF-104
* Aeritalia F-104S
* CL-1200 Lancer and Lockheed X-27
similar aircraft=
* Grumman F-11 Tiger
* Dassault Mirage III
* Northrop F-5
* Saunders-Roe SR.53
lists=
* List of fighter aircraft
* List of military aircraft of the United States
* List of F-104 Starfighter operators
see also=
* Century Series
* Bell XF-109

References

Notes

Bibliography

* Bowman, Martin W. "Lockheed F-104 Starfighter". Ramsbury, Marlborough, Wiltshire, UK: Crowood Press Ltd., 2000. ISBN 1-86126-314-7.
* Drendel, Lou. "F-104 Starfighter in action (Aircraft No. 27)". Carrollton, TX: Squadron/Signal Publications, 1976. ISBN 0-89747-026-5.
* Kinzey, Bert "F-104 Starfighter in detail & scale". Blue Ridge Summit, PA: TAB books, 1991. ISBN 1-85310-626-7.
* Pace, Steve. "F-104 Starfighter: Design, Development and Worldwide Operations of the First Operational Mach 2 Fighter". St. Paul, MN: Motorbooks International, 1992. ISBN 0-87938-608-8.
* Pace, Steve. "X-Fighters: USAF Experimental and Prototype Fighters, XP-59 to YF-23". St. Paul, MN: Motorbooks International, 1991. ISBN 0-87938-540-5.
* Reed, Arthur. "F-104 Starfighter – Modern Combat Aircraft 9". London: Ian Allan Ltd., 1981. ISBN 0-7110-1089-7.
* Upton, Jim. "Warbird Tech - Lockheed F-104 Starfighter". North Branch, MN: Specialty Press, 2003. ISBN 1-58007-069-8.

External links

* [http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=2311 XF-104 page on USAF National Museum site]
* [http://home.att.net/~jbaugher1/f104_1.html Joe Baugher XF-104 page]
* [http://www.vectorsite.net/avf104_1.html#m2 XF-104 on vectorsite.net]


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